Actuators has been used as external control means such as electromagnetic valves, lamps, relays, small DC motors for the purpose of controlling plants or equipment. Many of the actuators are driven by DC voltage, and the side to give instruction to the plant or equipment (hereafter referred to as the instruction side) is insulated from the side to perform measurement, drive, or control in the plant or equipment (hereafter referred to as the plant side) for the purpose of preventing affections on the human body or evading affections of noise depending on use. Signals sent from the instruction side and signals of measurement result sent from the plant side to the instruction side are insulated by photocouplers, signal insulation relays, insulation amplifiers, and insulation transformer. When electric power is needed, insulation transformer is adopted for the electric power source.
In recent years, there has been an increased demand for performing soundness diagnosis of circuit in the field of instrumentation and measurement for the purpose of raising reliability of the system by confirming soundness of output signals and circuit wiring, that is, by confirming whether actuators such as electromagnetic valves, lamps, relays, and small DC motors are operating correctly as instructed and whether there is a breaking of wire or short circuit occurred in the circuit.
FIG. 7 and FIG. 8 respectively shows an example of conventional drive circuit of an external control means consisting of an actuator such as an electromagnetic valve, lamp, relay, small DC motor, and that added with a circuit for diagnosing soundness of the drive circuit.
In FIG. 7, reference numeral 160 is a driving voltage signal for driving an actuator 163 such as an electromagnetic valve, lamp, relay, small DC motor (hereafter referred to as the object depending on circumstances), 161 is a signal insulation relay for insulating the plant side from the instruction side, and 162 is a DC electric power source for driving the actuator.
In FIG. 8, reference numeral 101 is an electric power source circuit for supplying electric power to a signal conversion circuit for current detection, 164 and modulating circuit 165. The power source circuit consists of a pulse generating circuit 103 for converting the electric power from the electric power source 102 into a pulse voltage, an insulation transformer 104 for transforming the voltage of the pulse voltage from the pulse generating circuit 103 and insulating the plant side from the instruction side, a rectifying circuit 105 for rectifying the pulse transformed by the insulation transformer 104, and a constant voltage circuit 106 for smoothing and rendering the rectified pulse into a constant voltage. A broken line denoted by reference numeral 107 indicates an insulation barrier. Reference numeral 164 is a signal conversion circuit for current detection, 165 is a modulating circuit, 166 is an insulation transformer, 167 is a demodulation circuit, and 168 is a read over current signal.
The driving voltage signal 160 in FIG. 7 is inputted to the signal insulation relay for insulating the signal, and electric power sent from the DC power source 162 provided separately is sent to the object 163, an actuator such as an electromagnetic valve lamp, relay, and small DC motor to drive it.
In the circuit provided with a circuit for performing soundness diagnosis shown in FIG. 8, it is similar as in the case of FIG. 7 that the DC power source 162 is provided to send electric power via the signal insulation relay 161 to the actuator (object) 163 to drive it. However, in the circuit of FIG. 8, there are provided an insulation amplifier consisting of the signal conversion circuit 164 for detecting the current in the actuator 163, modulating circuit 165 for converting the detected current into voltage, insulation transformer 166, and demodulating circuit 167 for converting the voltage signal into a current signal; and an electric power source circuit 101 consisting of the electric power 102, pulse generating circuit 103, insulating transformer 104, rectifying circuit 105, and constant voltage circuit 106; for the purpose of diagnosing the soundness of circuit such as whether the actuator 163 is operating as instructed and whether there is breaking of wire or short circuit occurred in the circuit.
The driving voltage signal 160 is inputted to the signal insulation relay 161 for insulating the signal to switch on the signal insulation relay 161, and electric power sent from the DC electric power source 162 is sent to the actuator (object) such as an electromagnetic valves, lamp, relay, and small DC motor to drive it, similarly to the case of FIG. 7. A current sent from the DC power source 162 via the signal insulation relay 161 is detected by the signal conversion circuit for current detection 164 and converted into a voltage signal, the voltage signal is modulated by the modulating circuit 165 to be converted into a modulated voltage signal (alternating voltage signal) and sent to the insulation transformer 166, then converted into a current signal by the demodulating circuit 167 in the instruction side, thus the current flown to the object 163 is outputted from the demodulation circuit 167 as a read over 168.
That is the conventional circuit provided with the function of diagnosing the soundness of circuit such as whether the actuator such as an electromagnetic valve, lamp, relay, and small DC motor used for the purpose of controlling a plant or equipment is operating as instructed, and whether there is a breaking of wire or short circuit occurred. With this conventional circuit construction for diagnosing operation status of the external control means, there have been problems as follows:
(A) An electric power source circuit and soundness diagnosing circuit must be added to perform soundness diagnosis separately from the circuit for transmitting the signal for driving the actuator, so, the number of parts increases and circuit construction becomes complicated, resulting in increased manufacturing cost.
(B) It is necessary to provide an additional circuit such as an excess current detecting circuit for the purpose of detecting occurrence of abnormality, and further to provide separately a safeguard such as a circuit protector or fuse against excess current flow.
Therefore, when intending to perform soundness diagnosis, it is inevitable with the conventional system that manufacturing cost is seriously increased, and the conventional system can not be adopted unless there is a strong demand to increase reliability in spite of increasing of manufacturing cost.
As to the art for detect braking of wire, there are disclosed for example in patent literature 1 (Japanese Laid-Open Patent Application No. 2006-023105) a method of detecting breaking of wire by applying a pulse signal to the wire, and comparing the current wave shape measured with the reference current wave shape to judge the presence or absence of breaking of wire from difference in both the wave shapes, and in patent literature 2 (Japanese Laid-Open Patent Application No. 2004-198302) a circuit for detecting breaking of wire by applying a pulse signal for checking via an impedance component to the signal wire for detecting breaking of wire, and comparing the signal obtained from the signal wire with the pulse signal for checking to judge the presence or absence of breaking of wire.
As to diagnosis of electric circuits, there is disclosed for example in patent literature 3 (Japanese Laid-Open Patent Application No. 8-005708) a method of diagnosing electric circuits and diagnosing device used for the method. With the method, conditions of electric apparatuses are diagnosed for the purpose of improving efficiency of diagnosis operation by facilitating measurement record management and further decreasing occurrence of man-caused errors, by reading out information written and stored in a nonvolatile memory concerning measurement results of characteristics or things concerning measurement of the electric apparatuses, or measurement results of characteristics or things concerning measurement of the electric apparatuses, and comparing the read-out information with the information of-the-moment concerning measurement results of characteristics or things concerning measurement of the electric apparatuses.
However, with the art taught in the patent literature 1 and 2 which relates to a detection of a breaking of wire in a circuit, means for applying pulse signals and a memory for memorizing reference current wave shape are needed, and with the electric circuit diagnosing device disclosed in the patent literature 3, a memory memorized information concerning measurement results of characteristics or things concerning measurement of the electric apparatuses is needed, and further a means for measuring characteristics of the circuit and a means for comparing the measurement result with the reference data, resulting in complicated composition. Therefore, problems cited in the items (A) and (B) cannot be solved by these arts.